The declared package does not match the expected package

Hi everyone,

I have a problem importing an external project. I go file->import->existing projects into workspace, choose the folder where the project is located and everything is imported - but the package names of the project don't seem to be what Eclipse expects. The package names all have a prefix:

prefix.packagename1
prefix.packagename2
etc.

But Eclipse expects

packagename1
packagename2
etc.

I don't really want to mess around with external code, so how do I tell Eclipse to create some kind of super-package "prefix"? Or what else can I do?

Okay... I forgot to mention that I'm also a noob and need serious hand-holding.
I just don't want to change the package names because I'm afraid of problems with external updates later. The whole thing came in a jar file, but adding that to the classpath doesn't help: It only adds another branch to my project containing class-files (the project comes with sourcecode and class-files in the same folders). What exactly should I bundle in a jar file and how do I do it?

Btw I don't know if that's easier than trying to get useful information out of me, but you could have a look at the project.
legacy.lclark.edu/~drake/Orego.html
The jar file is here:
webdisk.lclark.edu/drake/orego/
(the latest one)

I added it under configure build path->libraries. Unfortunately, it doesn't help because as I said, it only adds folders full of class files to my project. The problem with the unexpected package names persists.